Embodiments of the invention are directed to environmental control system bearing cooling flows and more particularly to energy recovery and efficiency of bearing cooling flows in environmental control systems.
Conventional aircraft environmental control systems incorporate an air cycle machine, also referred to as an air cycle cooling machine, for use in cooling and dehumidifying air for an aircraft cabin. Such air cycle machines may include two or more wheels disposed at axially spaced intervals along a common shaft. The wheels are part of, for example, a compressor rotor, a turbine rotor, a fan rotor, an additional turbine rotor, or an additional compressor rotor. In some cases the turbine or turbines drive both the compressor and the fan.
On aircraft powered by turbine engines, the air to be conditioned in the air cycle machine is typically compressed air bled from one or more compressor stages of the turbine engine. In conventional systems, this bleed air passes through the air cycle machine compressor where it is further compressed. The compressed air is passed through a heat exchanger to cool the compressed air sufficiently to remove moisture and dehumidify the air. The dehumidified compressed air is expanded in the turbine of the air cycle machine to both extract energy from the compressed air so as to drive the shaft and also to cool the expanded turbine exhaust air before it is supplied to the aircraft cabin as conditioned cooling air.
The air cycle machine may include one or more bearings. During operation, the bearings will heat up, and thus a cooling flow is passed through the air cycle machine that cools the bearings. This cooling air may be bleed air from one of the environmental control system heat exchangers. After passing through the air cycle machine, the bearing cooling air is passed or dumped into a RAM circuit that includes a fan.